DFC100 and GPSS

Like a recent "DFC100 and VNAV" post, we've noted a spike in questions about the DFC100 as certification approaches.  This post involves the DFC100 and GPSS mode.  Questions keep popping up about how to activate GPSS mode with the DFC100.

As you have probably noticed, there is no GPSS button on the DFC100 control panel.   This is intentional.  There is no standalone GPSS mode with a DFC100 - and there doesn't need to be one.

In a STEC 55X equipped airplane, GPSS had a few unique characteristics.  In this mode, the roll steering commands to the autopilot were coming completely from the 430/430Ws and not affected/computed by the Avidyne displays.  It was also a tighter lateral tracking mode enroute and these two characteristics led many pilots to rely heavily on that mode for coupled operations.

In a DFC100-R9 system, whenever "FMS" is the nav source as selected in the PFD page Primary Nav LSK, you are automatically getting roll steering and a tight GPS-based lateral tracking accuracy.  The DFC100 NAV mode takes its lateral steering commands from whatever is selected in the PFD page Primary Nav LSK.  If FMS is selected in Primary Nav, then the FMS is using a GPS-based signal to drive the autopilot NAV mode.  If NAV1 or NAV2 are selected, then the system is using the VHF-based signal to drive the autopilot NAV mode.

Let's use this thread to ask/answer and DFC100 GPSS related questions.   I'd like to think that the above explanation means there will not be any more GPSS related questions but we'll see......

Steve Jacobson
VP Product Management
Avidyne Corporation